The field of the present invention is that of an arrangement of a variable timed camshaft for an automotive internal combustion engine. More particularly, the present invention relates to an arrangement of an advance and retard pressurized fluid supply variable timed camshaft having for an automotive internal combustion engine.
Automotive vehicle engines with reciprocal pistons typically have a plurality of cylinder combustion chambers with the reciprocating pistons mounted therein. Each piston is pivotally connected with a piston rod, which is pivotally connected with a crankshaft. At an end of the crankshaft a timing gear is mounted. Typically, each cylinder has at least one intake valve and one exhaust valve. Both the intake valve and the exhaust valve are spring loaded to a closed position. Each intake and exhaust valve is associated with a rocker arm. To operate the valves, the rocker arms are moved by a set of contacting cam lobes. The cam lobes are mounted on an elongated member known as a camshaft. Attached at an extreme end of the camshaft is a camshaft pulley. The camshaft pulley is powered by the crankshaft via a timing chain or belt which is looped over the camshaft pulley and the crankshaft timing gear. Accordingly, the camshaft is synchronized with the crankshaft and the timing of the opening and closing of the intake and exhaust valves is fixed with respect to the position of the piston within the cylinder combustion chamber.
In an effort to improve the environment by decreasing polluting emissions and increasing vehicle gas mileage, it has become desirable to allow the timing of the cylinder valve operation to vary with respect to the piston position within the cylinder chamber. To provide for the variable valve timing operation, variable cam timing units (VCT) are provided on the camshaft. A dual oil feed vane-type variable cam timing unit provides an inner member or hub that is fixably connected to an end face of a camshaft. The hub has a series of vanes which are captured in cavities or pressure chambers provided in an outer member which is concentrically mounted on the hub. The outer member incorporates the camshaft timing pulley. The vanes circumferentially bifurcate the pressure chambers into an advance side and a retard side. A spool valve, fluidly communicative with the pressure chambers via the inner member and the camshaft, controls the fluid pressure in the advance side and retard side of the pressure chambers. Accordingly, the angular position of the timing pulley versus the crankshaft can be varied by controlling the fluid in the advance and retard pressure chambers.
In the prior art, the hub was connected by abutting contact to an end face of the camshaft by a threaded fastener. Typically, a set of retard pressurized fluid longitudinal bores were drilled into the end face of the camshaft. The hub had a set of retard pressurized fluid longitudinal bores aligned with the retard bores of the camshaft to allow fluid flow between the interface of the hub and the camshaft end face. The retard longitudinal bores of the camshaft, away from the camshaft end face (camshaft forward end), were intersected by radial cross-bores. The retard radial cross-bores fluidly communicated with an annular groove on the camshaft. The encircling groove on the camshaft fluidly communicated with the aforementioned spool valve which controls the fluid pressure in the advance and retard side in the pressure chambers between the hub and the timing pulley. In a similar manner to that described, there were additionally two longitudinal bores for the advance pressurized fluid. If the annular groove for the advance pressurized fluid was closer to the camshaft end face than the retard annular groove, the advance cross-bores were omitted and the advance longitudinal bores directly intersected with their respective annular groove. The longitudinal bores of the camshaft for the advance pressurized fluid also were aligned with longitudinal bores in the hub so that advance pressurized fluid could pass through the interface between the hub and the camshaft end face. When the hub was tightened by the fastener against the camshaft, the aforementioned retard and advance longitudinal bores in the camshaft had to be sealed with their respective bores within the hub. The sealing interface between the hub and the camshaft end face was dependent upon the machining and alignment between the hub and the camshaft. Accordingly, the sealing interface or clamping zone was not always predictable. Additionally, a required clamping load between the hub and the camshaft was dependent upon the sealing interface and therefore was not predictable.
Another disadvantage in the prior art was that there were four longitudinal bores extending between the camshaft end face and the hub. The two longest longitudinal bores had to be drilled past the annular groove nearest the camshaft end face. Accordingly, they had to be radially nearer the axial centerline of the camshaft than the other set of longitudinal bores. Additionally, there was a central or axial threaded bore to allow the fastener to be threadably connected with the camshaft. The presence of five axial bores drilled within the camshaft brought about a minimum required camshaft diameter which further defined the minimum journal bearing diameter allowed for a given camshaft.
U.S. Pat. No. 6,135,077, Moriya et al., provides a dual oil feed helical-type variable timing camshaft arrangement. In FIG. 2, one of the oil feeds passes through a fastener which attaches a hub member to the camshaft. Therefore, one of the pressurized fluid flows can pass through the axial centerline of the camshaft and the camshaft general bearing diameter can be minimized. However, the VCT unit of Moriya, et al. requires a sealing cap.
It is desirable to provide an arrangement of a VCT in which a journal bearing diameter of the camshaft can be held to a minimum value without the use of a sealing cap. It is desirable to provide a VCT arrangement wherein the clamping load between the inner member(hub)and camshaft is predictable and allowed to be along an annular ring on the face of the camshaft adjacent the camshaft outer diameter. Such an arrangement will provide the largest holding torque between the camshaft and VCT.
To make manifest the above delineated and other desires, the revelation of the present invention is brought forth. In a preferred embodiment, the present invention provides an arrangement of an advance and retard or dual oil feed variable timed camshaft for an automotive vehicle internal combustion engine. The arrangement includes a camshaft that has a radial side and an extreme longitudinal end face. The camshaft has a first passage fluidly connecting the camshaft end face with the radial side of the camshaft away from the end face. The first passage includes a longitudinal axial bore with a threaded portion.
The camshaft also has a second passage fluidly separated from the first passage connecting the camshaft end face with a radial side of the camshaft away from the end face. A hub is provided for abutting connection with the camshaft end face. The hub has a central opening intersecting with the first and second passages of the camshaft. The hub has at least first and second radial passages intersecting with the hub central opening. The hub first and second radial passages are axially spaced from one another. A timing pulley assembly is mounted on the hub having relative rotational movement with respect to the hub. At least one vane is connected to either the timing pulley assembly or to the hub. The timing pulley assembly and the hub define a pressure chamber therebetween which is divided into an advance angle space intersecting with the hub first radial passage and a second retard angle space intersecting with the hub second radial passage. A fastener is provided having a head and a threaded shank extending therefrom. The fastener shank has intersecting longitudinal and radial bores fluidly connecting the camshaft first passage with the hub first radial passage. The fastener head contacts with the hub to fasten the hub with the camshaft. A sealing member provides an interface between the shank of the fastener and the hub central opening to separate portions of the hub central opening exposed to the hub first radial passage from portions of the hub central opening exposed to the hub second radial passage.
It is an advantage of the present invention to provide an arrangement of a dual oil feed variable timed camshaft wherein a bolt fastener, which attaches an inner member or hub to the camshaft, also provides a fluid communicative path which extends radially outwardly.
It is also an advantage of the present invention to provide an arrangement of a dual oil feed variable timed camshaft wherein a single unitary fastener connects a hub with the camshaft and also wherein the fastener axially loads a sealing member which separates the advance and retard fluid paths.
It is also an advantage of the present invention to provide an arrangement of a dual oil feed variable timed camshaft, wherein the clamp zone between the hub and the end face of the camshaft is along a ring on the face of the camshaft adjacent the camshaft outer diameter providing the largest holding torque between the camshaft and hub and also providing a predictable clamping load.
The above-noted and other advantages of the present invention will become more apparent to those skilled in the art from a review of the invention as is provided in the accompanying drawings and detailed description.